Imaging apparatus (20, 44) includes an array (22) of optical sensing elements (24), characterized by a pitch, which is adapted to generate a signal in response to optical radiation that is incident on the elements. Objective optics (26, 46), which have an optical axis (134) and are characterized by a cylindrical symmetry about the axis, are arranged to focus the optical radiation from an object onto the array with a point spread function (PSF) having an extent greater than twice the pitch of the array at an optimal focus of the objective optics.